Characteristics of dissolved N2O and indirect N2O emission factor in the groundwater of high nitrate leaching areas in northwest China

Pan Huo; Yike Liu; Chunyan Xu; Xinyu Zhang; Haoxin Jia; Pengcheng Gao

doi:10.1016/j.scitotenv.2023.161641

Characteristics of dissolved N₂O and indirect N₂O emission factor in the groundwater of high nitrate leaching areas in northwest China

Sci Total Environ. 2023 Apr 10:868:161641. doi: 10.1016/j.scitotenv.2023.161641. Epub 2023 Jan 14.

Authors

Pan Huo¹, Yike Liu¹, Chunyan Xu¹, Xinyu Zhang¹, Haoxin Jia¹, Pengcheng Gao²

Affiliations

¹ College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi 712100, China.
² College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi 712100, China. Electronic address: pengcheng1969@nwsuaf.edu.cn.

PMID: 36649766
DOI: 10.1016/j.scitotenv.2023.161641

Abstract

Numerous studies have demonstrated high concentrations of dissolved N₂O and indirect N₂O emission factors in groundwater affected by agriculture. However, the characteristics of seasonal and vertical dimensional difference in groundwater in high nitrate leaching areas are relatively lacking. We monitored the concentrations of dissolved and wellhead N₂O of 23 groundwater wells over a one year period to understand the seasonal characteristics of dissolved and wellhead N₂O concentrations and indirect N₂O emission factors (EF₅) of the shallow and deep groundwater in a high nitrogen leaching area and analyze the reasons for their differences. The mean dissolved N₂O concentration in groundwater was 9.71 (9.03) μg/L, which was 1.5-fold higher during the wet season relative to the dry season. Furthermore, the leaching of soil N₂O caused by rainfall and irrigation could be a pivotal factor affecting seasonal variation in the dissolved N₂O. Shallow wells were found to have higher dissolved and wellhead N₂O concentrations compared with deep wells in all seasons. The low wellhead N₂O concentrations during the dry season were attributed to the seasonal decrease of the groundwater table and dissolved N₂O concentrations. We concluded that indirect N₂O emission factors did not vary in the vertical dimension but were higher during the wet season than that during the dry season. In addition, the mean indirect N₂O emission factor in the groundwater was 0.025 %, which was one order of magnitude below the current IPCC value (0.25 %). Thus, we proposed that such a low indirect N₂O emissions factor could imply a low indirect N₂O emission potential in groundwater with high dissolved oxygen and nitrogen loads. Our study further indicated that seasonal differences in dissolved N₂O concentrations and indirect N₂O emission factors should be considered when estimating the potential emissions of dissolved N₂O in groundwater.

Keywords: Dissolved N(2)O; EF(5g); Groundwater; Nitrate; Seasonal variation.